1. Field of the Invention
The present invention relates to the manufacturing of semiconductor wafers. More particularly, the present invention relates to chemical mechanical polishing (CMP) equipment for planarizing wafers during the manufacturing of semiconductor devices.
2. Description of the Related Art
Semiconductor devices are generally made by subjecting wafers to such selective and repetitive processes as photolithography, etching, diffusion, chemical vapor deposition, ion implantation and metal deposition processes. However, before being undergoing any of such processes, the wafers may be subjected to a chemical mechanical polishing (CMP) process that planarizes the wafers to make it easy to form circuit patterns on the surfaces of the wafers.
The CMP process involves uniformly distributing slurry onto a surface of a polishing pad that rotates at a high speed, and placing a surface of a wafer to be polished onto the surface of the polishing pad. As a result, the surface of the wafer chemically reacts with the slurry and is physically abraded by the slurry under the force of the high speed rotation of the polishing pad.
FIGS. 1 and 2 show conventional CMP equipment 10. The CMP equipment 10 includes a table 12 capable of rotating at a high speed, a polishing pad 14 mounted to the table 12, a slurry supply nozzle 16 disposed above the table 12 for supplying slurry onto the polishing pad 14 during the planarization process, and a cleaning solution supply nozzle 18 for supplying a cleaning solution onto the surface of the polishing pad 14 when the polishing process has been completed. The cleaning solution is used to remove slurry, etc., from the surface of the polishing pad 14.
The slurry and the cleaning solution are supplied through the slurry supply nozzle 16 and the cleaning solution supply nozzle 18, respectively, onto a central portion of the polishing pad 14. At either of these times, the polishing pad 14 is rotated at a uniform speed. Accordingly, the slurry or the cleaning solution gradually flows from the central portion of the polishing pad 14 toward the outer peripheral edge of the polishing pad 14, whereby the slurry or the cleaning solution is uniformly distributed over the surface of the polishing pad 14. Eventually, the slurry and the cleaning solution flow over the outer peripheral edge of the polishing pad 14.
Meanwhile, a surface of the wafer W to be planarized is placed against the surface of the polishing pad 14 by a polishing head unit 20 to which the wafer W is mounted. The polishing head unit 20 is situated to one side of the table. At this time, the wafer W is rotated at a high speed by a head 22 of the head unit 20 while the head 22 is moved over a region that is roughly shown by the dotted line 20a in FIG. 3. Simultaneously, the head 22 is raised/lowered to hold the wafer W proximate the surface of the polishing pad 14 or press the wafer against the pad 14 whereupon the polishing process takes place.
A conditioning unit 24 is also disposed beside the table 12. The conditioning unit 24 has a pad conditioner 26 for cutting the surface of the polishing pad 14 to maintain the surface uniform, i.e., so that the polishing pad 14 planarizes the surface of the wafer W uniformly. The pad conditioner 26 rotates at a high speed, opposite the polishing pad 14, and receives a constant downward force. The pad conditioner 26 is moved over a conditioning region shown by the dotted line 24a in FIG. 3 to condition the polishing pad 14 while the pad 14 rotates at a high speed.
The operation of the respective components will now be described.
First, the table 12 is rotated at a high speed under the command of a control signal applied thereto. At this time, the slurry supply nozzle 16 continuously supplies a constant amount of slurry onto the central portion of the rotating polishing pad 14 so as to be uniformly distributed across the entire surface of the polishing pad 14. Also, the polishing head unit 20 moves the wafer W round-trip across the head region 20a, with one entire surface of the wafer W proximate the surface of the polishing pad 14 or in contact therewith. Accordingly, the surface of the wafer W in contact with the slurry or the polishing pad 14 is polished by chemically reacting with and physically rubbing against the slurry.
However, the upper surface of the polishing pad 14 eventually becomes irregular due to the contact with the wafer W. The conditioning unit 24 is used to obviate the problems that such an irregular surface of the polishing pad 14 would otherwise create. Specifically, the conditioning unit 24 rotates the pad conditioner 26 at a high speed, places the pad conditioner 26 in contact with the polishing pad 14, and simultaneously moves the pad conditioner 26 back and forth across the conditioning region 24a. As a result, the pad conditioner 26 cuts the entire surface of the polishing pad 14 to planarize it to a given thickness.
Once the polishing process for the wafer W or the conditioning process for the polishing pad 14 is completed, the formerly supplied slurry and particles from the conditioned (cut) polishing pad 14 remain on the surface of the polishing pad 14. If allowed to stay there, the slurry and particles would scratch or negatively affect the uniformity of the next wafer W to be polished.
Therefore, a cleaning process is performed at the completion of the polishing process or at some other time at which the removal of various foreign substances from the surface of the polishing pad 14 is required. The cleaning process is executed by supplying a cleaning solution through the cleaning solution supply nozzle 18 onto a central portion of the polishing pad 14 while the pad rotates at a high speed. The cleaning solution thus gradually flows toward the outer peripheral edge of the pad 14 due to the centrifugal force created by the high speed rotation of the polishing pad 14. At this time, the slurry and various foreign substances on the polishing pad 14 are slid an upper surface of the polishing pad 14, and toward the outer peripheral edge thereof, by the flow of the cleaning solution. Finally, the slurry and various foreign substances entrained by the cleaning solution deviate are forced over the outer peripheral edge of the polishing pad 14.
However, the slurry and the various foreign substances not only flow along the surface of the polishing pad 14 to the outer peripheral edge of the polishing pad 14, but also are entrained in fumes that rise from the surface of the polishing pad 14. The particulate matter of these fumes are deposited throughout the CMP chamber C including on the walls of the chamber C and on respective components of the CMP equipment 6. The deposited slurry and various foreign substances accumulate and solidify over time. The solidified slurry and various foreign substances eventually flake off and fall onto the polishing pad 14 during a polishing process, whereby they scratch the wafer W being polished.
Furthermore, a sensor (not shown) is usually provided for checking whether a wafer W is present on an arm of a transfer device for loading/unloading the wafers W into and from the CMP equipment 10. If such a sensor is covered with the slurry and various foreign substances from the fumes produced in the chamber C, the sensor outputs erroneous information to the controller of the CMP equipment 10. The malfunction of the sensor in this way may result in a collision between the wafers W or between a wafer W and other components of the CMP equipment 10. Such collisions will damage or otherwise break the wafers W.
The CMP equipment 10 is thus cleaned periodically to prevent these and other problems that would otherwise be caused by the deposited and solidified slurry and foreign substances. This cleaning process is laborious and thus, requires much time. Also, the slurry and various solidified foreign substances produce dust, which poses a danger to the health of workers and pollutes the respective components of the CMP equipment 10.